Fibrous board products having improved surface

ABSTRACT

Fibreboards made from lignocellulosic fibres and painted with a water-based paint have a tendency to &#39;&#39;&#39;&#39;brown&#39;&#39;&#39;&#39; on the surface. Such browning is prevented by coating the surface of the fibreboard with a solution of a water-soluble salt of barium, calcium, strontium or lead prior to painting with a water-base paint. A preferred solution is one of chloride.

United States Patent Shisko 1 Mar. 11, 1975 FIBROUS BOARD PRODUCTS HAVING [56] References Cited IMPROVED SURFACE UNITED STATES PATENTS [75] Inventor: Walter S. Shisko, Ottawa, Ontario, 3,105,773 10/1963 Frank et al. 117/151 X Canada 3,536,578 10/1970 Brundige etal. 162/160 3,676,055 7/1972 Smith 117/60 X 1 Assigneer Domtar Limited, Montreal, Canada 3,676,182 7/1972 Smith 117/60 Filed June 19 1972 3,723,164 3/1973 Marton et a1 117/76 P 9 [21] Appl. No: 263,922 Primary Examiner-Michael R. Lusignan Attorney, Agent, or Firm-C. A. Rowley [30] Foreign Application Priority Data a ABSTRACT June 16,1972 Canada 144986 Fibreboards made from ligno-ceuulosic fibres and [52] U 5 CI W60 7H6 P 117/152 painted with a water-based paint have a tendency to l62/181 162/184 brown on the surface. Such browning is prevented [511 lm Cl B44d 1/092 by coating the surface of the fibreboard with a solu- [58] Field 76 P 71 R tion of a water-soluble salt of barium, calcium, stron- 1 17/148 i'' i A tium or lead prior to painting with a water-base paint.

A preferred solution is one of chloride.

3 Claims, N0 Drawings FIBROUS BOARD PRODUCTS HAVING IMPROVED SURFACE The present invention relates to fibrous board products having an improved surface and more particularly fibreboard having a surface rendered resistant to discolouration or browning".

BACKGROUND OF THE INVENTION The manufacture of fibreboard is well known. A slurry of lignocellulose fibres is supplied to a suitable forming apparatus such as a cylinder machine or a fourdrinier, and the fibres are formed into a sheet or mat of desirable thickness while the water is drained off. The sheet or mat so formed is further processed, viz. subjected to pressing, cut to required size and dried, and in most cases, painted. It is often further processed to suit any particular purpose it is designed to serve, for example, it may be perforated to a desired depth to give it sound absorbing properties or further cut to smaller size, and so on.

It has been the experience of many manufacturers that when the board so manufactured has been painted with a water-base paint, particularly a white paint, discolouration of the painted surface often occurs. This shows itself as a yellow or brown colour striking through the white paint, uniformly or in patches and appearing on the surface and rendering the surface unsightly. This discolouration is often referred to as browning. Browning may occur immediately after the board is painted and dried, but more often it appears later, often when the board is already in the hands of the customer, and sometimes only several months after installation. Understandably, it may cause considerable embarrassment to manufacturer and customer alike.

The cause of the phenomen is nor clearly understood, but it is believed to be due to the formation of certain water-soluble coloured materials from the noncellulosic constituents of the lignocellulose fibres. As is well known, the fibres used in the making of board are constituted in large part by groundwood or other highyield pulp obtained, for instance, by partly cooking wood chips with water or steam, with or without chemicals, followed by mechanicalrefining; such fibres generally contain substantial quantities of lignin as well as of other non'cellulosic materials, such as tannis, sugars and others. These seem to be the source of the coloured materials which, once formed, apparently diffuse through the layer of paint on the surface of the board and spread irregularly on said surface tending to mar its appearance.

DESCRIPTION OF THE PRIOR ART Hitherto, this discolouration could be prevented or avoided by painting the fibreboard with an oil-base paint. However, these paints are generally more expensive and more difficult to handle than water-base paints. As an alternative, several layers of water-base paint can be applied, one on top of the other, to a thickness sufficient to prevent the migration ofthe colouring matter to the surface of the board. However, this also entails substantial expense and in many cases is uneconomical to use.

SUMMARY OF THE INVENTION I have now found that browning can be substantially completely eliminated by a simple process wherein the surface of the board, prior to painting, is treated with an aqueous solution of salts of certain heavy metals and then processed in the usual manner.

The present invention provides a fibrous board product from lignocellulosic fibres which is resistant to browning, said fibrous product having at least one surface thereof coated with an aqueous solution of a water-soluble salt of a metal of the group consisting of barium, calcium, strontium and lead.

The present invention also provides a process for making a fibrous board product from lingocellulosic fibres which is resistant to browning, said process comprising applying to a surface of said board a water solution of a salt of a metal of the group consisting of barium, calcium, strontium and lead.

DESCRIPTION OF PREFERRED EMBODIMENTS According to the invention, the board is first produced in the usual manner, i.e. by forming a fibrous mat of desired thickness and basis weight, pressing the formed sheet of mat (the ultimate density being largely determined in this step), cutting it to desired size and drying it by any convenient method. The dried board is conveyed to a suitable station where the water solution ofa metal salt, herein described, is applied to a surface of the board. The solution is applied by any suitable means, e.g. by roller application, by brushing, or where convenient by spraying. The solution may be applied to the .wet board, i.e. before it is dried, but it is generally preferred to dry the board first and apply the solution onto the surface of the dried board.

The solutions suitable for use in this invention are solutions of certain salts of barium, calcium, strontium and lead. Only water-soluble salts of these metals are contemplated and preferably those providing a colourless solution; such solution, upon being applied on the surface of the board and is instrumental in the prevention of browning. Examples of suitable salts are barium chloride, barium acetate and barium nitrate, as well as the chlorides, acetates and nitrates of calcium and strontium, lead nitrate and lead acetate. Preferred use is made of barium chloride.

The concentration of the solution may vary within wide limits, but should desirably not be less than 2% and preferably between 5 and 20%. Higher concentrations may be used, if desired, up to the limit of solubility of the salt in water. It is often desirable to prepare the salt solution with a small quantity of a thickening agent as an additive, the effect of which is to facilitate the distribution of the solution over the surface of the board or to improve the film forming properties of the solution. Various organic compounds may be used as such additives, examples being starch, dextrin, cellulose ethers, urea-formaldehyde, polyvinyl acetate, animal glue and the like. A quantity of additive between 0.5 and 5% by weight (based on total solution) has been found generally suitable. It may be desirable to add to the solution a small quantity of a wetting agent. such as the non-ionic surface active agents sold under the name IGEPAL, or the like.

The solution is applied to the surface of the board to form a continuous layer thereon and then the board may be painted and the painted surface dried in any suitable manner. If desired, the surface of the board with the solution applied thereto may be dried before paint is applied, and then painted and dried in the usual manner; and in some cases the manufacturer will produce an unpainted board having a coating of the solution of this invention applied thereto and dried, leaving the painting to the user.

The quantity of solution that should be applied to obtain an effective cure to browning will depend on the concentration of salt in the solution, on the quantity of additive, on the severity of the browning to be overcome and similar factors. I have found quantities between l and pounds per thousand square feet to be generally satisfactory, but quantities may have to be adjusted to particular conditions, such as the already mentioned concentration of the solution, the nature of the surface of the board, the degree of browning to be overcome and so on.

EXAMPLE I The following formulation was prepared:

Water 364 lbs.

Polyvinyl acetate 18 lbs.

(at 55% solids) Barium chloride 68 lbs. Wetting agent 1 lb.

(Polyoxyethylene condensate of alkylphenol known in commerce as lgepal C0630) The solution thus prepared was applied to the surface ofa fibre-board produced in the usual manner from lignocellulosic fibres. The fibres were produced from commercial chips and shavings (from lumber mills) by a very short alkaline cook and subsequent mechanical refining. The fibres were formed into a mat on an Oliver machine, the mat was passed to a Downington press, cut to suitable lengths and placed in a drier for l 1 /2 hours. At this stage the solution was applied in an amount of about 20 lbs per 1000 sq. ft. of surface of the board and the board was then painted with a water base latex paint (polyvinyl acetate as binder) and dried in the usual way by passage under infra-red light.

The board so produced was inspected from time to time over a period of 24 months and showed substantially no sign of browning. A board produced from the same material and exactly in the same manner except for the surface application of the solution of this invention showed severe browning after two weeks.

EXAMPLE [I Formulations were prepared as follows:

consisting of a dextran material sold under the name Y-69 Fuller") EXAMPLE Ill Formulations were prepared as follows:

I ll

1150 lbs 5 lbs Water Thickening agent (a hydroxyethyl cellulose sold by the Hercules Chemical Company under the trade name Natrosol 250 HR) Wetting Agent (lgepal C0630) Strontium Nitrate Lead Nitrate llb llb lbs l25 lbs These solutions were applied to fibreboard as in Example l, with substantially similar results. I

While examples have been provided to explain the invention and to enable one skilled in the art to follow it, it will be understood that various changes in the composition, steps and materials may be made by those skilled in the art within the scope of the invention as expressed in the claims. While the invention has been described with particular reference to fibreboard, it will be understood that it could be applied to other manufactured articles made from lignocellulose fibres and having a problem with browning as herein described.

I claim:

1. ln a fibrous board made from lignocellulosic fibres and having on at least one surface thereof a coat of water-base resin paint, the improvement for rendering said surface resistant to browning which comprises a coating on said surface underlying said coat of waterbase resin paint, said coating consisting ofa dried aqueous solution ofa water-soluble salt of the group consisting of the chloride, acetate and nitrate of barium, the chloride, acetate and nitrate of strontium, the chloride, acetate and nitrate of calcium, lead nitrate and lead acetate, the concentration of said salt solution being at least 2%.

2. A fibrous board product according to claim 1 wherein said salt is barium chloride.

3. A fibrous board product according to claim 2 wherein said product is fibreboard. 

1. IN A FIBROUS BOARD MADE FROM LIGNOCELLULOSIC FIBERS AND HAVING ON AT LEAST ONE SURFACE THEREOF A COAT OF WATER-BASE RESIN PAINT, THE IMPROVEMENT FOR RENDERING SAID SURFACE RESISTANT TO BROWNING WHICH COMPRISES A COATING ON SAID SURFACE UNDERLYING SAID COAT OF WATER-BASE RESIN PAINT, SAID COATING CONSISTING OF A DRIED AQUEOUS SOLUTION OF A WATER-SOLUBLE SALT OF THE GROUP CONSISTING OF THE CHLORIDE, ACETATE AND NITRATE OF BARIUM, THE CHLORIDE, ACETATE AND NITRATE OF STRONITIUM, THE CHLORIDE, ACETATE AND NITRATE OF CALCIUM, LEAD NITRATE AND LEAD ACETATE, THE CONCENTRATION OF SAID SALT SOLUTION BEING AT LEAST 2%.
 1. In a fibrous board made from lignocellulosic fibres and having on at least one surface thereof a coat of water-base Resin paint, the improvement for rendering said surface resistant to browning which comprises a coating on said surface underlying said coat of water-base resin paint, said coating consisting of a dried aqueous solution of a water-soluble salt of the group consisting of the chloride, acetate and nitrate of barium, the chloride, acetate and nitrate of strontium, the chloride, acetate and nitrate of calcium, lead nitrate and lead acetate, the concentration of said salt solution being at least 2%.
 2. A fibrous board product according to claim 1 wherein said salt is barium chloride. 